In a conventional non-cooperative cellular network, base stations (BSs) and mobile stations (MSs or ‘users’) in a cell communicate signals without considering stations and mobile stations in adjacent cells. Because the cells can overlap and the RF spectrum is shared, signals in adjacent cells can interfere with each other, particularly at mobile stations.
Therefore, wireless cellular networks are usually interference-limited because the power of interfering signals is much larger than the power of noise, and spectral efficiency gains are limited by intercell co-channel interference (CCI).
The resulting interference could be reduced by appropriate versions of multiple access (MA) schemes such as TDMA, FDMA and CDMA, e.g., by re-using frequency bands not used in every cell. However, those schemes decrease the spectral efficiency of the network. If the BSs cooperate by concurrently transmitting signals for different MSs, then the spectral efficiency of the network can be improved. However, the improved spectral efficiency in BS cooperation requires additional overhead, because the BSs need to exchange information for the cooperation to be effective. Typically, a network backbone or infrastructure is used to exchange this information. Different types of cooperation can be used, depending on whether channel state information (CSI) and data, or the different users are available at the BSs.
In the following, to give a concrete example of a system, BS cooperation in WiMax networks (Worldwide Interoperability for Microwave Access) is described. WiMAX is based on the IEEE 802.1.6e standard. As an alternative to wired broadband like cable and DSL, WiMAX is intended to provide high-speed broadband communication via a wireless channel. The radius of a typical WiMAX cell is expected to be about three to tell kilometers, with a deliver capacity of up to 40 Mbps per channel. WiMAX uses orthogonal frequency division multiplexing (OFDM).